1. Field of the Invention
The present invention relates to display devices provided with a display panel for color display such as a liquid crystal display or an organic electroluminescent (EL) display.
2. Description of the Related Art
Such display devices are generally provided with a display panel that produces color images with a large number of pixels arranged regularly. These display devices are widely used as display screens such as those for personal computers, mobile telephones, portable information devices and thin television sets. Here, in order to achieve color display, each pixel is generally composed of subpixels of light's three primary colors, namely, red (R), green (G) and blue (B). The term “subpixel” refers to a display unit that can be individually controlled to be driven.
Colors of subpixels contained in one pixel are not particularly limited to the light's three primary colors as long as color display is achieved. For example, the colors of subpixels may be three primary colors, namely, cyan (C), yellow (Y) and magenta (M), that serve as complementary colors for the light's three primary colors; the colors of subpixels may include the light's three primary colors and the complementary three primary colors.
Scanning lines (gate lines) extending in a row direction (in the horizontal direction of a display screen) and signal lines (source lines) extending in the column direction (in the vertical direction of the display screen) are connected to subpixels. Subpixels are driven by source and gate signals applied from a controller through the scanning lines and signal lines, and thus color display is achieved.
In order to produce high-definition, high-quality color images, a variety of configurations of subpixels are conventionally employed since color images are significantly affected such as by the configuration of subpixels of which pixels are composed. In general, the arrangements of three-color subpixels, when the light's three primary colors (R, G and B) are employed, include a stripe arrangement, a mosaic arrangement, a square arrangement and a delta arrangement.
In the stripe arrangement, as shown in FIG. 33, three subpixels (each having a different color) of one pixel are arranged in a row, and this is repeated in a row direction; such a row is repeatedly arranged in the column direction such that the subpixels of the same colors are arranged in the column direction. In the mosaic arrangement, as shown in FIG. 34, three subpixels (each having a different color) of one pixel are arranged in a row, and this is repeated in the row direction; each row is shifted by one subpixel relative to the next in the row direction such that subpixels are arranged one color after another in the column direction.
In the square arrangement, as shown in FIG. 35, four subpixels (with the three colors being used such that one red (R), one blue (B) and two green (G) subpixels are selected) of one pixel are arranged in two rows to form a square shape, and this is repeated in a row direction; two such rows are arranged in the column direction. In the delta arrangement, as shown in FIG. 36, three subpixels (each having a different color) of one pixel are arranged in two rows to form a delta shape, and this is repeated in a row direction while being inverted for each repetition; each row is shifted by one-half of the subpixel relative to the next in the row direction such that two such rows are repeatedly arranged in the column direction.
Theses color arrangements of subpixels are selectively used for different products; in particular, the stripe arrangement is often used in display devices for television sets and personal computers required to have high definition.
A source signal having a voltage whose positive/negative polarity is periodically inverted is applied to each signal line. In order to reduce the generation of display flickering called flicker, a polarity-inversion drive method is generally employed in which source signals having voltages whose polarities alternate or vary from one subpixel to the next along a row are applied. In order to reduce flicker occurring in the column direction, source signals having voltages whose polarities alternate from one subpixel to the next along a column are applied.
Display devices today are required to further improve brightness. One way to fulfill this requirement is to form one pixel from four-color subpixels composed of three subpixels of the light's three primary colors (R, G and B) and one additional high-brightness subpixel of white (W) or the like and to arrange such pixels (for example, see patent documents 1 to 5). In this way, the subpixel of the fourth color improves the brightness of the pixel, with the result that the basic performance of a display device is improved.    Patent document 1: JP-A-H02-118521    Patent document 2: JP-A-H11-295717    Patent document 3: JP-A-H10-010998    Patent document 4: JP-A-2004-102292    Patent document 5: JP-A-2005-062869
In a case where the subpixel of the fourth color is added to one pixel to improve brightness, however, the following problem occurs. The addition of the subpixel of the fourth color to each pixel increases the number of source drivers for each pixel by the subpixel added. The source driver mentioned herein refers to a device that outputs a drive signal to a signal line; one source driver is provided for each signal line.